Transcript Chemistry: The Study of Change

교재: 레이먼드 창, 일반화학, 11판.
Chemistry:
The Study of Change
Chapter 1
제 1장 - 화학
1.
2.
3.
4.
5.
6.
7.
화학이란
과학적 방법
물질, 분류, 상태
물질의 성질
측정
수, 유효숫자
과학적 표기법, 인자 표시법
불을 다루는 학문(火學)이 아니라
숭례문 火災
화학이란?
변화(變化)
학문(學問)
Chemistry:
The Study of Change
Chemistry: A Science for the 21st Century
• Health and Medicine
• Sanitation systems
• Surgery with anesthesia
• Vaccines and antibiotics
• Gene therapy
•Energy and the Environment
• Fossil fuels
• Solar energy
• Nuclear energy
Chemistry: A Science for the 21st Century
• Materials and Technology
• Polymers, ceramics, liquid crystals
• Room-temperature superconductors?
• Molecular computing?
• Nano-materials and non-metal conductors.
• Food and Agriculture
• Genetically modified crops
• “Natural” pesticides
• Specialized fertilizers
The Study of Chemistry
Macroscopic
Microscopic
ⅹ108
1 cm
100 pm
The scientific method is a systematic
approach to research
A hypothesis is a tentative explanation for a
set of observations
tested
modified
A law is a concise statement of a relationship
between phenomena that is always the same
under the same conditions.
Force = mass x acceleration
A theory is a unifying principle that explains
a body of facts and/or those laws that are
based on them.
Atomic Theory
Chemistry In Action:
Primordial Helium and the Big Bang Theory
In 1940 George Gamow hypothesized that the universe
began with a gigantic explosion or big bang.
Experimental Support
• expanding universe
• cosmic background radiation
• primordial helium
Chemistry is the study of matter and the
changes it undergoes.
Matter is anything that occupies space and
has mass.
A substance is a form of matter that has a
definite composition and distinct properties.
liquid nitrogen
mercury
silicon wafer
A mixture is a combination of two or more substances
in which the substances retain their distinct identities.
1. Homogenous mixture – composition
of the mixture is the same throughout.
soft drink, milk, solder
2. Heterogeneous mixture – composition is not
uniform throughout.
cement,
iron filings in sand
Physical means can be used to separate a mixture
into its pure components.
distillation
An element is a substance that cannot be
separated into simpler substances by chemical
means.
• 114 elements have been identified
• 82 elements occur naturally on Earth
gold, aluminum, lead, oxygen, carbon
• 32 elements have been created by scientists
technetium, americium, seaborgium
A compound is a substance composed of atoms
of two or more elements chemically united in fixed
proportions.
Compounds can only be separated into their
pure components (elements) by chemical
means.
Water (H2O)
Ethanol (C2H6O)
Hydrogen Chloride (HCl)
Classifications of Matter
Matter
Separation by
physical methods
Mixtures
Heterogeneous
mixtures
Homogeneous
mixtures
Compounds
Pure Substances
Separation by
chemical methods
Elements
A Comparison: The Three States of Matter
The Three States of Matter
gas
liquid
solid
Physical or Chemical?
A physical change does not alter the composition
or identity of a substance.
sugar dissolving
ice melting
in water
A chemical change alters the composition or
identity of the substance(s) involved.
The Hindenburg
hydrogen burns in
air to form water
Extensive and Intensive Properties
An extensive property of a material depends upon
how much matter is is being considered.
• mass
• length
크기성질
• volume
An intensive property of a material does not
depend upon how much matter is is being
considered.
• density
• temperature
• color
세기성질
Matter - anything that occupies space and has mass.
mass – measure of the quantity of matter
SI unit of mass is the kilogram (kg)
1 kg = 1000 g = 1 × 103 g
weight – force that gravity exerts on an object
weight = c × mass
A 1 kg bar will weigh
on earth, c = 1.0
1 kg on earth
on moon, c ~ 0.1
0.1 kg on moon
International System of Units (SI)
SI 기본 단위
물리
이름
SI 유도 단위(일부)
기호
길이
미터
m
질량
킬로그램
kg
시간
초
s
전류
암페어
A
온도
켈빈
K
물질
량
몰
mol
광도
칸델라
cd
유도량
이름
기호
넓이
제곱미터
m2
부피
세제곱미터
m3
속력, 속도 미터 매 초
m/s
가속도
미터 매 초 제곱
m/s2
밀도
킬로그램 매 세제곱미터
kg/m3
농도
몰 매 세제곱미터
mol/m3
광휘도
칸델라 매 제곱미터
cd/m2
Table 1.3 Prefixes Used with SI Units
Prefix
Symbol
Meaning
Length(m)
Time(s)
peta-
P
1015
Ly(9×1015)
tera-
T
1012
Sun-Jupiter
giga-
G
109
mega-
M
106
kilo-
k
103
Time to run 5km
deci-
d
10-1
심장박동
centi-
c
10-2
milli-
m
10-3
빗방울 반지름
micro-
μ
10-6
cell
nano-
n
10-9
big molecules
pico-
p
10-12
femto-
f
10-15
atto-
a
10-18
zepto
z
10-21
조선시대 평균수명(32년)
대한민국 길이
10 일
빛이 300mm를 지나는
시간
nucleus
molecular vibration
Volume – SI derived unit for volume is cubic meter (m3)
1 cm3 = (1 × 10-2 m)3 = 1 × 10-6 m3
1 dm3 = (1 × 10-1 m)3 = 1 × 10-3 m3
1 L = 1000 mL = 1000 cm3 = 1 dm3
1 mL = 1 cm3
Density – SI derived unit for density is kg/m3
1 g/cm3 = 1 g/mL = 1000 kg/m3
mass
density =
volume
m
d= V
A piece of platinum metal with a density of 21.5
g/cm3 has a volume of 4.49 cm3. What is its mass?
m
d= V
m = d × V= 21.5 g/cm3 × 4.49 cm3 = 96.5 g
K = 0C + 273.15
273 K = 0 0C
373 K = 100 0C
0F
9
= 5 × 0C + 32
32 0F = 0 0C
212 0F = 100 0C
Convert 172.9 0F to degrees Celsius.
9
= 5 × 0C + 32
0F – 32 = 9 × 0C
5
0F
5 × (0F – 32) = 0C
9
0C = 5 × (0F – 32)
9
0C = 5 × (172.9 – 32) = 78.3
9
Chemistry In Action
On 9/23/99, $125 million Mars Climate Orbiter entered Mar’s
atmosphere 100 km (62 miles) lower than planned and was
destroyed by heat.
NASA, JPL, Lockheed Martin
1 lb = 1 N
1 lb = 4.45 N
In this day and age when the
metric system is the
measurement language of all
sophisticated science, two
measurements systems should
not be used. Only the metric
system should be used because
that is the system science uses.
Scientific Notation
The number of atoms in 12 g of carbon:
602,200,000,000,000,000,000,000
6.022 × 1023
The mass of a single carbon atom in grams:
0.0000000000000000000000199
1.99 × 10-23
N × 10n
N is a number
between 1 and 10
n is a positive or
negative integer
Scientific Notation
568.762
0.00000772
move decimal left
move decimal right
n>0
n<0
568.762 = 5.68762 × 102
0.00000772 = 7.72 × 10-6
Addition or Subtraction
1. Write each quantity with
the same exponent n
2. Combine N1 and N2
3. The exponent, n, remains
the same
4.31 × 104 + 3.9 × 103 =
4.31 × 104 + 0.39 × 104 =
4.70 × 104
Scientific Notation
Multiplication
1. Multiply N1 and N2
2. Add exponents n1 and n2
Division
1. Divide N1 and N2
2. Subtract exponents n1 and n2
(4.0 x 10-5) × (7.0 × 103) =
(4.0 × 7.0) × (10-5+3) =
28 × 10-2 =
2.8 × 10-1
8.5 × 104 ÷ 5.0 × 109 =
(8.5 ÷ 5.0) × 104-9 =
1.7 × 10-5
Significant Figures(유효숫자)
• Any digit that is not zero is significant
1.234 kg
4 significant figures
• Zeros between nonzero digits are significant
606 m
3 significant figures
• Zeros to the left of the first nonzero digit are not significant
0.08 L
1 significant figure
• If a number is greater than 1, then all zeros to the right of the
decimal point are significant
2.0 mg
2 significant figures
• If a number is less than 1, then only the zeros that are at the
end and in the middle of the number are significant
0.00420 g
3 significant figures
Q. How many significant figures are in
each of the following measurements?
24 mL
2 significant figures
3001 g
4 significant figures
0.0320 m3
3 significant figures
6.4 × 104 molecules
2 significant figures
560 kg
2 significant figures
Significant Figures(유효숫자)
Addition or Subtraction
The answer cannot have more digits to the right of the decimal
point than any of the original numbers.
89.332
+1.1
90.432
3.70
-2.9133
0.7867
one significant figure after decimal point
round off to 90.4
two significant figures after decimal point
round off to 0.79
Significant Figures(유효숫자)
Multiplication or Division
The number of significant figures in the result is set by the original
number that has the smallest number of significant figures
4.51 × 3.6666 = 16.536366 = 16.5
3 sig figs
round to
3 sig figs
6.8 ÷ 112.04 = 0.0606926 = 0.061
2 sig figs
round to
2 sig figs
Significant Figures(유효숫자)
Exact Numbers
Numbers from definitions or numbers of objects are considered
to have an infinite number of significant figures
The average of three measured lengths; 6.64, 6.68 and 6.70?
6.64 + 6.68 + 6.70
= 6.67333 = 6.67 = 7 ?
3
Because 3 is an exact number
Accuracy – how close a measurement is to the true value
Precision – how close a set of measurements are to each other
accurate
&
precise
precise
but
not accurate
not accurate
&
not precise
Dimensional Analysis Method of Solving Problems
1. Determine which unit conversion factor(s) are needed
2. Carry units through calculation
3. If all units cancel except for the desired unit(s), then the
problem was solved correctly.
given quantity × conversion factor = desired quantity
given unit ×
desired unit
given unit
= desired unit
Dimensional Analysis Method of Solving Problems
Q. How many mL are in 1.63 L?
Conversion Unit 1 L = 1000 mL
1000 mL
1.63 L ×
= 1630 mL
1L
1L
L2
1.63 L ×
= 0.001630
1000 mL
mL
Q. The speed of sound in air is about 343 m/s. What is
this speed in miles per hour?
conversion units
meters to miles
seconds to hours
1 mi = 1609 m
1 min = 60 s
1 mi
60 s
m
×
×
343
s 1609 m
1 min
1 hour = 60 min
60 min
mi
×
= 767
hour
1 hour
1983년 7월23일, Air Canada Flight 143
from Montreal to Edmonton
needs 22,300 kg of jet fuel to fly
Story 1: On 23 July 1983, Air Canada Flight 143 ran completely out of fuel about
halfway through its flight from Montreal to Edmonton. Fuel loading was
miscalculated through misunderstanding of the recently adopted metric system.
For the trip, the pilot calculated a fuel requirement of 22,300 kg. There were
7,682 liters already in the tanks.
Problem 3 - If a liter of jet fuel has a mass of 0.803 kg, how much fuel needed to
be added for the trip?
mass/unit volume = 0.803
kg/L
Answer:
In order to calculate how much more fuel had to be added, the crew needed
to convert the quantity in the tanks, 7,682 L, to a weight, subtract that figure
from 22,300 kg, and convert the result back into a volume (L).
7,682 L × (0.803 kg/ 1 L)= 6,169 kg
22,300 kg – 6,169 kg = 16,131 kg
16,131 kg × ( 1 L / 0.803 kg) = 20,088 L of jet fuel. <= volume required.
mass/unit volume = 1.77
lb/L
Between the ground crew and flight crew, however, they arrived at an incorrect
conversion factor of 1.77, the weight of a liter of jet fuel in pounds. This was the
conversion factor provided on the refueller's paperwork and which had always
been used for the rest of the airline's fleet.
Their calculation produced:
7,682 liters × (1.77 pounds/liter) = 13,597 which they interpreted as kilograms
but was actually the fuel mass in pounds! Then they continued the calculation:
22,300 kg – 13,597 'kg' = 8,703 kg
8,703 kg ÷ 1.77 = 4,916 L <= actual volume fueled.
….so they were actually 15,172 L short of fuel! (20,088 L-4,916 L)
Story 2: On September 23, 1999 NASA lost the $125 million Mars Climate
Orbiter spacecraft after a 286-day journey to Mars. Miscalculations due to the
use of English units instead of metric units apparently sent the craft slowly off
course -- 60 miles in all. Thrusters used to help point the spacecraft had, over
the course of months, been fired incorrectly because data used to control the
wheels were calculated in incorrect units. Lockheed Martin, which was
performing the calculations, was sending thruster data in English units (pounds)
to NASA, while NASA's navigation team was expecting metric units (Newtons).
Problem 1 - A solid rocket booster is ordered with the specification that
it is to produce a total of 10 million pounds of thrust. If this number is
mistaken for the thrust in Newtons, by how much, in pounds, will the
thrust be in error? (1 pound = 4.5 Newtons)
Answer:
10,000,000 'Newtons' × ( 1 pound / 4.448 Newtons) = 2,200,000
pounds instead of 10 million pounds so the error is a 'missing' 7,800,000
pounds of thrust…an error that would definitely be noticed at launch!!!
Story 3: On January 26, 2004 at Tokyo Disneyland's Space Mountain,
an axle broke on a roller coaster train mid-ride, causing it to derail. The
cause was a part being the wrong size due to a conversion of the
master plans in 1995 from English units to Metric units. In 2002, new
axles were mistakenly ordered using the pre-1995 English specifications
instead of the current Metric specifications.
Problem 2 - A bolt is ordered with a thread diameter of 1.25 inches.
What is this diameter in mm? If the order was mistaken for 1.25 cm,
by how many mm would the bolt be in error?
Answer:
1- inch = 25.4 mm so 1.25 inches × (25.4 mm/ 1 inch) = 31.75 mm.
Since 1.25 cm = 12.5 mm, the bolt would delivered 31.75 - 12.5 = 19.25 mm
too small!